Tire Size Spec Topic is solved

[93SCMax]

Just to clarify, even though your V70 and my V70 are at opposite ends of the P2 production (2001 vs 2007), any changes in chassis, wheel, or suspension/steering hardware during that time were negligible and would not affect my ability to install 235/45/17s?

My 2001 V70 T5 came stock from the factory with 235/45/17's. JRL is correct that any of the mentioned tire sizes will fit. I will also confirm that the 235/45/17's will rub the front inner fender well when making hard turns, and that the turning radius of the car is wider than normal...but she does ride and look good with this size tire.

[jbeebo]

I have a 2005 S60 non-turbo that came with factory 195/65-15 and can also confirm 235/45-17 will fit. I replaced the wheels with used Volvo OEM 17's and new 235/45-17 tires. I did need to change the steering lock limiters, and adding a 10mm hub-centric wheel spacer with longer wheel studs. After these changes the tire will just barely rub on the wheel well at full lock and there is no negative impact to the turning radius.

Regarding tire pressure, the door plate is a good starting point but might need some tweaking. A simple way to check that you've got the correct pressure for your particular tires with your particular loading condition is to use the chalk line test. Setting tire pressure by this method will ensure even wear across the contact patch, and thus maximum surface area on the road and maximum tire life.

[prwood]

Regarding tire pressure, the door plate is a good starting point but might need some tweaking. A simple way to check that you've got the correct pressure for your particular tires with your particular loading condition is to use the chalk line test. Setting tire pressure by this method will ensure even wear across the contact patch, and thus maximum surface area on the road and maximum tire life.

Random question - when I go on YouTube and look for tire pressure chalk test, almost all of the videos are from people with trucks, SUVs, or other off-road vehicles. Is there a reason they'd be more likely to do this than a typical street car driver?

[jbeebo]

The technique is universally applicable but I do believe there is a reason why you see this technique on trucks & offroad vehicles more than passeger cars. I think this is due to the huge variation in tire sizes, wheel sizes and loading conditions. For example, a 33" tire could well be found on a stripped down 1988 Toyota 4x4 pickup, or a Jeep CJ or a Yukon or a decked out Suburban. These vehicles have vastly different weights and 33" is not the factory size so to have a hope of getting close to the "correct" tire pressure you do this test. Further, truck tire construction also varies widely, from 2 ply polyester sidewalls for street comfort oriented 33" tires all the way to 4 ply belted and reinforced sidewalls to prevent rock slices and punctures from ruining your day offroad. Identical 30psi in these two examples will create totally different contact patch for a given loading condition.

Pass cars are a bit different story. There's not as much variation in vehicle weights or tire sizes or tire construction which can fit on a given car so going off the OEM recommendations shouldn't be horrible - but it's likely not optimum. By setting pressure to maximize contact patch for that particular tire/wheel/vehicle combo you should be close to optimum (at least from a tire wear perspective). From here you can vary pressure to suit your particular goals whether it be adjusting the understeer characteristics, or ride harshness, or noise, or tracking, etc.

[JRL]

You use common sense.
Any tire pressure between the two pressures listed will be fine.
If the ride is too rough, you drop it a couple of lbs. If you think it's too soft, add a couple of lbs. You have to experiment for a couple of days
Again, USE COMMON SENSE and use the pressure YOU like, Each car and each brand and type of tire is and rides differently from each other.
There are very decent small gauges you can buy for 25 bucks, keep one in your car and always check pressures when cold

[Georgeandkira]

It's also common sensical to add 10% before long trips. I call it "Highway Hard" and it's no secret.
Drop 'em back to your normal when the trip is over.

This bit of involvement will heighten your sensitivity to tire pressure. And yes, I mean that.
If more people had done that we wouldn't have had to pay for TPMS systems.
$400 when the batteries die?....Thanks to fat bottomed (lazy) motorists.

[zanzabar]

RE: tire pressure - every tire manufactured has a maximum pressure stamped on the side of it. I've seen anywhere from 40-53 psi on the tires I've had on my passenger cars. Forget what it says on the car, how do they know what tire you happen to have mounted? Those pressures are chosen to sell cars that feel nice and cushy off the dealer lot, and probably in collusion with the tire companies to sell more tires since lower pressure will wear them out faster. I typically run near the max pressure in an effort to maximize fuel economy and tire life. The tires on my cars last FOREVER with this technique, well past their warrantied mileage every time. I don't mind the extra feedback from small road bumps, etc, which is definitely there if you pay attention. If you don't pay attention you'll never notice.

[prwood]

Ok. I appreciate everyone providing me with a first-class education in tire size and specs. You have all been helpful, and thank you for hanging in there with me. However, as is the case so many times, answers lead to other questions... my questions so far have been centered around *tires*, but now I have some questions about *wheels*, in my quest to become master of this car. I am sure some of you are thinking that in the end, none of this stuff will really matter, and some of it is probably guesswork, and that's probably true, but my brain is still craving the knowledge.

1. I measured the diameter of the wheels that are currently installed. They are 17" diameter. The currently installed tires have a printed diameter of 16". My assumption is that, when installed, the tires, being made of flexible rubber, were simply stretched an extra inch to fit over the 17" wheels, and that this is within the normal specification of the tires and is standard practice. Is that how things work? Or is it not even considered a "stretch" to put 16" tires on 17" wheels?

2. If the stock tire size was 195/65R15, would the stock wheels have been 15"? Or would they have been 16" with the 15" tire stretched onto them (as above). And then at some point someone upgraded to 17" wheels with 16" tires stretched onto them?

3. If I shop for tire+wheel packages at TireRack.com for my year/make/model/trim, I get 16" as "OE" Diameter, 17" as "+1" diameter and 18" as "+2" diameter. If that's what they're offering, can I assume that all of those sizes would work? Would someone use an 18" wheel mostly for looks, or are there practical reasons to use a wheel that's 2" bigger than OE?

[JRL]

If the tire is a 16" tire, you have 16" wheels ... PERIOD
As for #3 you need to start reading about tires and wheels in general, sizes and why some car have larger wheels and some do not
Good grief!

Stretch a tire? What the hell does that mean? You actually think this is possible!!!
READ what tire rack says. If you go thru their website and read, they will explain. Don't read only two lines then ask us the most ridiculous questions possible. They do a good job of explaining tires and wheels if you actually read everything.

Every time you go up a wheel size in a plus 1 configuration the car will ride stiffer, you will be able to bend your wheels easier, but it will look "cooler"!!
If you go plus 2, good luck, you will think you have no suspension left and the tires will blow out much easier, now you will EASILY bend more wheels not to mention an 18" tire will cost about twice the cost of a 16" tire.

With the right LARGER tire and wheel combination, a car usually will handle better but the ride on a rougher road suffers big time. The bigger the wheel the smaller the sidewall, ergo no tire "cushion", at all!
There always are trade offs

[prwood]

OK! Topic solved. "Just read stuff."